In chemical liquid treatment systems, variation in the effect of a chemical liquid is indicated by a function of time or duration of chemical liquid treatment (discharge). In conventional chemical liquid treatment systems, the number of wafers (workpieces) was calculated for each processing lot and the treatment time was calculated to achieve the optimum performance or effect of the chemical liquid based on a pre-fetched function between liquid effect and the number of wafers to be processed.
The above described arrangement may be useful in processing lots where there are no significant deviations in the chemical treatment time from the pre-fetched function. However, when there are significant differences in the treatment time between the processing lots, the treatment time will deviate significantly from the pre-fetched function and affect the accuracy of treatment time calculation, which in turn may render the subsequent processing lots to progress abnormally.